1. Field of the Invention
This invention generally relates to a charge forming apparatus for supplying a mixture of fuel and air to an internal combustion engine, and more particularly to a charge forming apparatus or carburetor which is adapted to control fuel to be fed to a mixture passage by means of a flexible diaphragm according to the demand of an internal combustion engine.
2. Description of the Prior Art
A carburetor of the type of controlling fuel by means of a float or float-type carburetor has been conventionally used, for example, in an engine for an automobile and is required not to substantially tilt and fall down.
A carburetor of the type of controlling fuel by means of a diaphragm or diaphragm-type carburetor has been typically used in a two-cycle engine for a chain saw, a mowing machine, a snowmobile, a boat or the like and has an advantage capable of controlling fuel in any posture.
The conventional diaphragm-type carburetor generally comprises a body formed therein with a passage for a mixture of air and fuel in which a venturi and a throttle valve are arranged, a fuel pump having a diaphragm adapted to be actuated by an engine pulse, a passage arranged to outward extend from the outlet of the fuel pump, a fuel chamber having one of the walls thereof defined by a flexible diaphragm, a valve controlled by the flexible diaphragm so as to open or close the inlet of the passage communicated with the fuel chamber, and a supply passage for feeding fuel in the fuel chamber to a slow port and an idle port opened toward a main nozzle and a throttle valve each communicated with a venturi of the mixture passage. In the diaphragm-type carburetor constructed as described above, the fuel pump and a fuel pressure control mechanism are arranged on the surface of the body, and the diaphragms and a cover member are fixed on the body.
In view of the foregoing, it will be noted that the diaphragm-type carburetor is characterized in its small-sized and compact structure. Also, in the diaphragm-type carburetor, the idle port and slow port serve to feed fuel to the mixture passage due to high negative pressure generated not on the side of the substantially closed throttle valve but on the side of an engine at the idling or slow rotational speed of the engine and the main nozzle acts to feed fuel to the mixture passage due to high negative pressure generated at the venturi at a medium or high engine speed. Such a fuel supply system is substantially the same as that in the float-type carburetor.
In the diaphragm-type carburetor, only the construction which is capable of carrying out the supply of a mixture of air and fuel to an engine in a manner to prevent the occurrence of trouble in a two-cycle engine of small displacement such as engine malfunction has been required. Thus, the diaphragm-type carburetor fails to rapidly increase fuel corresponding to a rapid increase in air flowing through the mixture passage when the substantially closed throttle valve is rapidly opened, so that such an increase in engine speed as expected by a driver may not be obtained in the diaphragm-type carburetor.